Enteroendocrine cells protect the stem cell niche by regulating crypt metabolism in response to nutrients

Abstract

Background and aimsThe intestinal stem cell niche is exquisitely sensitive to changes in diet, with high fat diet, caloric restriction, and fasting resulting in altered crypt metabolism and intestinal stem cell function. Unlike cells on the villus, cells in the crypt are not immediately exposed to the dynamically changing contents of the lumen. We hypothesized that enteroendocrine cells (EECs), which sense environmental cues and in response release hormones and metabolites, are essential for relaying the nutrient status of the animal to cells deep in the crypt. MethodsWe used the tamoxifen-inducible VillinCreERT2 mouse model to deplete EECs (Neurog3fl/fl) from adult intestinal epithelium and we generated human intestinal organoids from wild-type and NEUROG3-null human pluripotent stem cells. We used indirect calorimetry, 1H-NMR metabolomics, mitochondrial live imaging, and the Seahorse bioanalyzer to assess metabolism. Intestinal stem cell activity was measured by proliferation and enteroid-forming capacity. Transcriptional changes were assessed using 10X Genomics single-cell sequencing. ResultsLoss of EECs resulted in increased energy expenditure in mice, an abundance of active mitochondria, and a shift of crypt metabolism to fatty acid oxidation. Crypts from mouse and human intestinal organoids lacking EECs displayed increased intestinal stem cell activity and failed to activate phospho-S6 ribosomal protein, a marker for activity of the master metabolic regulator mammalian target of rapamycin (mTOR). These phenotypes were similar to those observed when wild-type mice were deprived of nutrients. ConclusionsDeletion of EECs recapitulated a fasting phenotype despite normal levels of ingested nutrients. These data suggest that EECs are required to relay nutritional information to the stem cell niche and are essential regulators of intestinal metabolism.